Field Test Report: 175-Watt Solar Panel with Integrated Water Heating System
This summer, we tested our new 175-watt SunPower solar panel with an integrated water heating system over a six-week cruise in Northern Lake Huron (latitude ~46°). The panel was connected to an EP Xtra-N 20 amp MPPT Controller and mounted on a CMP pole system, allowing for adjustable tilt and rotation. By rotating the panel three times daily (morning, midday, evening), we optimized the sun angle, achieving around 30% more efficiency than a fixed horizontal panel.
Performance Overview:
Our daily energy consumption averaged 70 amp-hours (AH), equivalent to 850 watt-hours (WH). This covered a 24/7 refrigerator/freezer, evening LED lighting, charging for phones and laptops, and daily use of radios and instruments. A 75-amp Balmar alternator with a smart regulator handled additional loads, such as the windlass, while underway.
With two new 100AH CMP LiFePo4 batteries in our house bank and one as a starter battery, our system was fully charged by 1 PM on most sunny days. This performance matched our prior 160-watt panel's output but with additional charging capacity.
Key Findings:
-
Efficient Charging: The EP Xtra-N MPPT controller with a remote display was easy to program and reliably efficient, delivering up to 10 amps during peak morning hours. By afternoon, it shifted to float mode, maintaining the charge without overloading.
-
Excess Power Utilization: In the afternoons, we used excess solar power with an inverter to run an ice maker, a luxury we enjoyed without significant impact on battery reserves.
-
Increased Efficiency from Panel Rotation: Rotating the panel, especially in the morning, significantly improved power generation compared to a fixed position.
-
Shading Impact: Shading from the backstay or mast, though minimal, reduced panel output by as much as 40%.
-
Integrated Water Heating: The water heating system performed well, raising the temperature in our 6-gallon water tank from 60°F to 105°F within 2-3 hours on sunny days. The heat exchanger cooled the panel by at least 20°F, improving solar efficiency. Insulated tubing between the panel and water heater further enhanced the system’s performance.
Data Summary:
| Panel Wattage | Condition | Average WH/day | Average AH/day | Max WH (24h) | Max AH (24h) |
|---|---|---|---|---|---|
| 175W | Sunny to Mostly Sunny | 900 | 69 | 1280 | 98 |
| Cloudy to Mostly Cloudy | 435 | 33 | 570 | 44 | |
| 160W | Sunny to Mostly Sunny | 700 | 54 | 1210 | 93 |
| Cloudy to Mostly Cloudy | 400 | 31 | 770 | 59 |
Observations:
- Output varies with cloud cover and battery state of charge. The system’s maximum output was capped due to full battery charge by early afternoon.
- Average AH/day is a rough estimate calculated by dividing WH by 13V.
- This setup met all cruising power needs without auxiliary solar or shore power.
In conclusion, the 175-watt solar panel with integrated water heating successfully met our power demands while offering enhanced efficiency through tilt and rotation adjustments. We’ll provide more insights on our battery system soon. For further details on our water heating design, refer to our previous blog.